It is well known in the industry to use a pocket conveyor to convey loose bulk material such as coal, stone, sand, grain, etc., when the material must be conveyed vertically or at very steep angles. One type of pocket conveyor for this use utilizes a flexible side wall type of rubber belting. This type of belt consists of a flat, reinforced rubber, base belt to which side walls constructed of corrugated shaped reinforced rubber are attached and between the two side walls, cross-flights or cleats are attached at regular intervals along the length of the belt to form troughs or pockets where the bulk material can be deposited.
The common method used to construct a steep angle or vertical conveyor of this type requires the flexible side wall belt to be bent around a series of pulleys or deflection wheels as shown in the prior art design illustrated in FIG. 1. When the belt must be bent in a direction that allows the bottom of the flat base belt to contact the pulley, a cylindrical-shaped pulley that extends across the full width of the base belt can be used; however, if the belt must be bent in the opposite direction, deflection wheels that contact the external surface of the base belt, only on the portion of the base belt that extends beyond the outside width of the side walls are used. The two deflection wheels are attached to a common shaft and the shaft is supported by bearings located outside each of the deflection wheels. The outside diameter of the deflection wheels must be large enough to allow the connection shaft to pass across the side walls that assist in forming the pockets that carry the bulk material. Therefore, in these prior art arrangements, the width of the flat base belt must be sufficiently wide to allow a portion of the base belt to extend laterally beyond the width of the two side walls. In these prior art constructions, the base belt extended laterally beyond the width of the two side walls approximately 10 to 18 inches. As a consequence, a portion of the width of the base belt is not utilized in cooperation with the sidewalls in forming the pockets or troughs.
In addition, when the belt must be bent around deflection wheels to redirect the belt, the maximum allowable belt tension is much less than when the belt is bent around a full-width cylinder shaped pulley. This is due to the fact that if the belt is bent around the deflection wheels, the total belt tension stress is concentrated near the edges of the base belt. On the other hand, if the belt is bent around a full width cylindrical pulley, the total belt tension stress is evenly distributed across the full-width of the base belt. Moreover, when the belt is bent around deflection wheels, the possibility exists that the belt will collapse down between the two deflection wheels if the belt tension exceeds the lateral strength of the belt. This may cause severe belt damage, or total destruction of the belt as well as loss of operation of the conveyor.
In addition, conventional vertical conveyors that are used to carry bulk material have a section of the flexible side wall belt travelling in a horizontal direction where the material is loaded onto the belt at the bottom of the lift, and another section of the belt travelling in a horizontal direction where the material is discharged at the top of the lift. This arrangement requires the belt to be bent around both full-width cylinder pulleys and deflection wheels. The maximum lift that can be achieved with this type of conveyor for any given belt strength is usually limited by the maximum belt tension sustainable where the belt wraps around the deflection wheels at the top of the lift. This tension is created by the weight of the vertical portion of the belt suspended from the deflection wheels at the top of the lift. Consequently, the length of the endless conveyor belt in prior art devices was considerably limited.
There is a growing need for vertical conveyors with very high lifts, often exceeding 600 feet, and the weight of this type of belt can be as much as 75 pounds per foot. Therefore, the resulting belt tension at the location of the deflection wheels at the top of the lift often can exceed 45,000 pounds. This belt tension approaches a load range where there is no belt available that has sufficient cross strength to operate properly. Another disadvantage of many prior art vertical conveyors is that they require support structure to be constructed over the entire length of the vertical run of the belt. When high vertical runs are required, it is generally time consuming and economically inefficient to construct a support structure for the conveyor that spans the entire vertical run.
In view of the above, there remains a need for a steep angle or vertical conveyor capable of traversing significantly high vertical runs that does not require the use of deflection wheels nor intermediate support structure.
There is also a need for a vertical conveyor system that can utilize the full tensile strength of the belt wherein all bends in the belt can be supported with full width cylindrical pulleys, therefore achieving a greater vertical lift. In addition, there is a need for the vertical conveyor system capable of traversing significant vertical runs that uses a less expensive base belt due in part to the fact that the overall width of the conveyor can be less than a conveyor system that requires deflection wheels. In addition, because the tension created by the belt is distributed over the entire width of the belt due to its full contact with the pulley, stronger and generally more expensive belts are not required.